Using Graphene to Lower the Cost and Footprint of LEDs

Photonics SpectraNov 2016
A white LED (WLED) has been developed using a hybrid metal-organic framework (MOF) material, which provides electrically driven white light emission with a continuous spectrum that matches well with natural sunlight. It could offer an economical, environment-friendly alternative to WLEDs whose development depends on the photon down-conversion of phosphors containing rare-earth elements.

To reduce the footprint and cost of WLEDs, researchers from National Taiwan University and Academia Sinica designed a direct WLED derived from a strontium-based MOF, graphene and inorganic semiconductor hetero-junctions. Testing of the device showed that the WLED’s emission spectrum was continuous, similar to natural sunlight. This is in contrast to currently commercially available WLEDs, which are comprised of three discrete colors (red, green and blue), and which can make the colors of the objects they illuminate appear distorted.

The researchers attribute the successful demonstration of MOF-based, electrically driven white light emission to several factors, including an appropriate band alignment between the MOF and semiconductor layer and to the unusual properties of graphene, including its excellent conductivity properties, its transparency, and the small effective mass necessary for the efficient injection of free carriers into a light-emitting active layer.

Widespread use of low-power, long-lasting LEDs in the U.S. could save nearly 348 terawatt-hours by 2027, an amount comparable to the annual output of 44 power plants, according to the U.S. Department of Energy. WLEDs are currently made with rare-earth elements and mining these minerals can be costly and produce toxic waste. Additionally, existing commercial methods for producing WLEDs involve multiple components and steps that can reduce efficiency and quality.

Together with environmentally friendly materials and a low-cost fabrication process, this timely discovery may be useful in the development of solid-state lighting and in reducing global energy consumption.

The nonthermal conversion of electrical energy into light in a liquid or solid substance. The photon emission resulting from electron-hole recombination in a PN junction is one example. This is the mechanism employed by the injection laser.